It is well known that well streams containing a mixture of fluids such as crude oil, condensate, formation water and gas during transportation may react and form solid hydrates resulting in i.e. blocked pipelines. To avoid and or limit the formation of these, hydrate inhibitors are added to the well stream prior to transportation. One often applied hydrate inhibitor is mono-ethylene glycol (MEG); other applicable hydrate inhibitors include glycol compounds with other substituents, as well as kinetic hydrate inhibitors or a combination thereof. The term kinetic refers to the effect of the inhibitor lowering the reaction rate of the hydrate forming reactions.
Hydrate inhibitors such as MEG are valuable chemicals and the recycling thereof provides reduced costs. A number of different steps and methods for separating MEG for reuse are known in the art. An obstacle for the regeneration process is degradation of the inhibitor at high temperatures which limits the possibility to use heating to obtain separation.
The recovered well stream will comprise not only the desired hydrocarbons, hydrate inhibitor, employed chemicals such as pH stabilizer and formation water, but also different ions dissolved from the formation. Traditional hydrate inhibitor recovery and reclamation systems have been developed to remove ions in the form of precipitated salts from the recovered hydrate inhibitor to control the salt concentration and allow for continued reuse of the hydrate inhibitor. The most common precipitated salts are chlorides, carbonates or hydroxides of Na, K, Ca, Mg, Fe or Ba. These precipitated salts are not considered especially harmful and the safe handling thereof can be relatively easily secured. Recently, however there has been discovered a number of formations which comprise heavy metals including mercury in such a form that the mercury ions are included in the well stream. In a traditional system the mercury ions will follow the hydrate inhibitor into the reclamation system and be precipitated in the form of mercury salts together with the other salts present in the rich hydrate inhibitor stream. However the separated salts will be a mixture comprising mercury salts and the total salt mixture must be treated as hazardous waste. In a standard traditional MEG reclamation system the amounts of salts removed per day is in the range 1 to 20 tonnes/day. The main part of the salts is NaCl. If heavy metal salts are introduced in this mixture then the total salts produced become hazardous waste that requires special treatment. This is very demanding especially on offshore installations.